EN
We prove that Brownian motion on an abstract Wiener space B generates a locally equicontinuous semigroup on $C_b(B)$ equipped with the $T_t$-topology introduced by L. Le Cam. Hence we obtain a "Laplace operator" as its infinitesimal generator. Using this Laplacian, we discuss Poisson's equation and heat equation, and study its properties, especially the difference from the Gross Laplacian.